(1) Field of the Invention
The present invention relates to the field of intervertebral disk prostheses.
The present invention relates more particularly to an intervertebral prosthesis of the type formed at least of one core which is positioned between an upper plate and a lower plate, said prosthesis furthermore comprising at least one outer casing.
(2) Prior Art
Intervertebral prostheses of this type are already known from the prior art.
There is thus proposed in U.S. Pat. No. 5,674,296 a vertebral disk endoprosthesis comprising a core, preferably an elastic core, and rigid elements with concave inner surfaces which at least partly surround the core. The endoprosthesis also comprises a sealing element which is formed of flexible material and is fixed to the rigid elements and surrounds the core.
This vertebral disk endoprosthesis (18) comprises a flexible core (20, 24), rigid concave/convex plates (30, 32, 34) arranged above and below the core, a relatively rigid peripheral packing ring (22) which surrounds the core (20, 24), and a sealing member (110) made of a flexible material which is attached to the concave/convex plates and surrounds the core and the packing ring.
Each concave/convex plate has a relatively constant thickness in cross section and has on the one hand a convex outer surface for engaging in the adjacent bone structure which has previously been drilled and on the other hand a corresponding concave inner surface for holding the resilient body of the core.
In this prosthesis, the shape of the inner faces of the plates is identical to the shape of the adjacent core and the core is thus strictly immobile.
The prostheses of the prior art are not satisfactory since they do not make it possible to guide and cushion the displacements of the underlying and overlying vertebrae in the same way as anatomical disks.